Can You Bend a Pencil? Fun with Grandchildren.

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A pencil “slashed” by the light refraction in a bowl of water (Photo credit: Wikipedia)

Can You Bend A Pencil?

In this activity, it appears that you have bent a pencil without touching it.

Materials:

Pencil (a straw works fine, too)

Water

Glass

Instructions:

Fill a water glass about 2/3 full of water.

Put a pencil in the glass, allowing it to lean against the side of the glass.

What Should Happen?

The pencil will appear to be bent at the water line.

That is, the part of the pencil underwater does not appear to be in a straight line with the part of the pencil above the water.

Why Is This Happening?

Light refracts, or bounces back to our eyes, at a different rate when it is going through water and when it is going through air.

It is similar to the phenomenon we saw in an earlier experiment when light refracted, or broke up into its respective colors, to make a rainbow, because it traveled through water and air at different speeds.

What Else Shows the Difference Between Air and Water and Light?

If you put a flat object in the water, like a ruler, you will see a slightly different effect.

The top part of the ruler will appear narrower than the part of the ruler in the water.

If you change the container, however, from a round water glass to a square glass container, like a vase, the bent effect you saw with the pencil happens again.

Why Is This?

The round glass acts like a convex lens, magnifying the light that comes from the flat, wide ruler that is underwater.

Again, the way the light is concentrated is different for air and water because of the different speeds that light travels through air and water.